I need recommendations for a balanced-power transformer(s) for use in U.S. 115-125VAC (i.e., a transformer model/manuf./DigiKey part no./etc.) Something with the following config. will work:
Thx in advance for any info you can provide.
An externally hosted image should be here but it was not working when we last tested it.
Thx in advance for any info you can provide.
You didn't specify what size you need. Here's the smallest one at Digikey:
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=237-1269-ND
and here's the largest:
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=237-1273-ND
Personally, I would just search on eBay for an "isolation transformer". Just make sure that the primaries & secondaries are flexible enough for you to wire how you need them. You should be able to beat those prices. I think even Mouser is cheaper for the US, but not for Canada because of the high shipping charges.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=237-1269-ND
and here's the largest:
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=237-1273-ND
Personally, I would just search on eBay for an "isolation transformer". Just make sure that the primaries & secondaries are flexible enough for you to wire how you need them. You should be able to beat those prices. I think even Mouser is cheaper for the US, but not for Canada because of the high shipping charges.
leadbelly said:
Thx for digging those up. I checked eBay but didn't find much at this time. For any of the Triad models you noted above, I assume the config will be a "Series Connection" (see their datasheets); this will output 1/2 of 120VAC. But I don't see a center-tapped ground lug on the Triad models -- a requirement from the schematic I posted originally.
I would look in nearby surplus stores. Lots of slightly used industrial transformers are available. (These are sometimes called "Control Transformers") You can also use a 240 Volt transformer if you run it at 1/2 it's rated power.
I use what I believe is a couple KVA-rated 220 to 440 VAC isolation transformer to step 120 VAC down to 60. I got it free from a scrap dealer friend. If I leave it plugged in operating a 600w resistive load, it overheats after a couple of hours. I wonder, a little, if part of the problem could be due to how long it was left outside.
hollowman said:
You need to wire both the primaries and secondaries in series, and then it will give you what you need.
I'm not sure I understand your question about a "center-tapped ground lug". You need to jumper the secondaries, this will create the center tap. Then just jumper this to your ground.
It wouldn't hurt to read up a bit on AC power supplies. It's a complex subject and you can't know too much.
Transformer connections
Thx for your reply.
WRT wiring the secondaries, I assume this means 11 and 8 will be connected both to themselves and ground. See image below..
(Sorry if this sounds trivial/redundant/obvious. But given the "high" voltages, I want to make sure nothing burns up! I agree that AC power supplies are a complex subject and one can't know too much.)
leadbelly said:
Thx for your reply.
WRT wiring the secondaries, I assume this means 11 and 8 will be connected both to themselves and ground. See image below..
(Sorry if this sounds trivial/redundant/obvious. But given the "high" voltages, I want to make sure nothing burns up! I agree that AC power supplies are a complex subject and one can't know too much.)
Re: Transformer connections
Yes, that's correct. And on the primary side 5 and 2 will be jumpered and the AC hot and neutral on 6 and 1.
hollowman said:
Yes, that's correct. And on the primary side 5 and 2 will be jumpered and the AC hot and neutral on 6 and 1.
Re: Re: Transformer connections
Cool. Thx for confirming that.
I'm now wondering whether it's more economical (and/or simpler) to create an isolated (outboard) balanced-transformer-based power station. I'm not sure whether every component benefits from balanced/isolated power -- not so much as to justify the addit. cost. Is, e.g., digital gear more in need of balanced/isolated power than analog?
leadbelly said:
Cool. Thx for confirming that.
I'm now wondering whether it's more economical (and/or simpler) to create an isolated (outboard) balanced-transformer-based power station. I'm not sure whether every component benefits from balanced/isolated power -- not so much as to justify the addit. cost. Is, e.g., digital gear more in need of balanced/isolated power than analog?
Re: Re: Re: Transformer connections
Personally, I'm not sure whether any component benefits from balanced power. 🙂
But no point starting a new debate on that one, just search for the most recent thread debating it.
hollowman said:
Personally, I'm not sure whether any component benefits from balanced power. 🙂
But no point starting a new debate on that one, just search for the most recent thread debating it.
Electrone said:
A 2 KVA transformer with 440 VAC input voltage may only be good for 0.545 KVA with 120 VAC input voltage.
Or maybe it's not a 2 KVA transformer! That size transformer might weigh 30 or 40 pounds. Or if it has multiple windings maybe some are mis-wired.
Re: Re: Transformer connections
I recently acquired the first one from DK you suggested. Wired it "correctly" -- I think -- but am getting 280VAC at the output (DMM probes at pins 12 & 7). My input (household) voltage is 123VAC and I also get 280VAC with probes at the input pins 1 & 6 when 2 & 5 are jumpered as suggested.
Just to remind everyone...2 is connected to 5, 11 is connected to 8, and both of those juctions are connected to a common (earth) GND.
DMM at pins 11 and 12 or 7 and 8 yield a strange 140VAC, which is a bit too high.
I need 110 - 125 VAC!
Thx for any info anyone can provide.
leadbelly said:
I recently acquired the first one from DK you suggested. Wired it "correctly" -- I think -- but am getting 280VAC at the output (DMM probes at pins 12 & 7). My input (household) voltage is 123VAC and I also get 280VAC with probes at the input pins 1 & 6 when 2 & 5 are jumpered as suggested.
Just to remind everyone...2 is connected to 5, 11 is connected to 8, and both of those juctions are connected to a common (earth) GND.
DMM at pins 11 and 12 or 7 and 8 yield a strange 140VAC, which is a bit too high.
I need 110 - 125 VAC!
Thx for any info anyone can provide.
An isolation transformer becomes very useful when servicing the mains live section of equipment, it's a must for anybody doing that kind of job regularly.
For that purpose I use four 1KVA toroids with 230V primaries and dual 60V secondaries, and this allows me to get 60V, 120V, 180V and 240V. There is a 20A variac feeding these transformers for finer voltage adjustment. I need this setup because I do a lot of high power off-line SMPS work.
I fail to see the the point of operating audio equipment with isolated or balanced power in everyday use, though.
For that purpose I use four 1KVA toroids with 230V primaries and dual 60V secondaries, and this allows me to get 60V, 120V, 180V and 240V. There is a 20A variac feeding these transformers for finer voltage adjustment. I need this setup because I do a lot of high power off-line SMPS work.
I fail to see the the point of operating audio equipment with isolated or balanced power in everyday use, though.
Re: Re: Re: Transformer connections
That doesn't make much sense to me. Have you made other connections? If your household power is 123VAC then that is what you should be connecting across pins 1 & 6, and that is what you should be measuring. Pins 2 & 5 are jumpered and isolated; not connected to anything else.
hollowman said:
That doesn't make much sense to me. Have you made other connections? If your household power is 123VAC then that is what you should be connecting across pins 1 & 6, and that is what you should be measuring. Pins 2 & 5 are jumpered and isolated; not connected to anything else.
You still didn't state the size that you needed, at least what I could find. You might try the discounted ones at Equitech:http://www.equitech.com/products/specials.html
Another solution: Just use an isolation transformer without a center tap and use a resistive or capacitive voltage divider to make the effective impedance of each side to ground about equal.
Still getting 144VAC on secondary
Thx for everyone's response.
On the primary, I orig. had 2 + 5 (the junction of these two connected to common ground). I removed the ground connection, and now have 123VAC measured on 2 and 5.
I'm still getting 144VAC on secondary at 12 and 7; half that (72VAC) when I put leads on 11 or 8 to 7 or 12.
I have both Triad transformers, noted by leadbelly earlier. But right now I'm only experimenting with the smaller unit. This will ultimately be used in a Philips CDP.
Thx for everyone's response.
On the primary, I orig. had 2 + 5 (the junction of these two connected to common ground). I removed the ground connection, and now have 123VAC measured on 2 and 5.
I'm still getting 144VAC on secondary at 12 and 7; half that (72VAC) when I put leads on 11 or 8 to 7 or 12.
I have both Triad transformers, noted by leadbelly earlier. But right now I'm only experimenting with the smaller unit. This will ultimately be used in a Philips CDP.
You need an isolation transformer just for a CD player ?
(TX definitely is the place to be for MOSFETs, Sugarland express tickets are likely offered at Christie's only)
(TX definitely is the place to be for MOSFETs, Sugarland express tickets are likely offered at Christie's only)
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